Ophthalmic lens



Feb. 14, 1928. 1,659,197

A. E. GLANCY OPHTHALMIC LENS Filed Feb. 2. 1925 Patented Feb. 14, 192s.

ANNA ESTELLE GLANCY, 0F SCUTHIBRIDGE, MASSACHUSETTS, ASSIGNOR TO AMERI- CAN OPTICAL COMPANY, OF SOUTHBRIDGE, MASSACHUSETTS, A VOLUNTARY ASSOCIATION OF MASSACHUSETTS.

, OPHTHALMIC LENS.

Application filed. February 2, 1925. Serial No. 6,309.

This invention relates to new and useful improvements in ophthalmic lenses, and has particular reference to a corrected prismatic lens and to a process for the production oi the same.

A most important object of the invention to produce a prismatic lens which shall be corrected for spherical and astigmatic error. i j

A second object of the invention is to produce a prismatic ophthalmic lens which shall have the prism desired, and whose geometrical center shall not differ in power from the prescribed power as is usually customary in prismatic lenses produced by deccntration.

Another object of the invention is to provide a blank from which can be cut prismatic ophthaln'iic lenses, the said blank having a center power correctedto produce a minimum amount of error at a decentered point, which is to be the geometrical center of the finished lens.

Still another objectof the invention is to provide a process whereby a blank may be formed for a prismatic ophthalmic lens having a prism of any given power, and which will give the most eflicient vision for a prismatic lens of that power.

Other objects and advantages of my invention will become apparent during the course of the following description taken in connection with the accompanying drawing.

In the drawing, wherein for the purpose of illustration I have shown the preferred.

embodiment of my invention, and in which like numerals designate correspondingparts throughout all views of the same; i Figure 1 is a front elevation of a lens blank used in my process, Figure 2 is asimilar view showing the second step in the process.- p

Figure 3 is a similar view showing the third step in my process andthe location of the center of the new lens. Figure 4 is a similar view showing the fourth step of my process.

l igureb is a front elevation of; a lens blank when the same has been ground to size, and illustrating the fifth step of my process.

Figure 6 shows the completed blank from which the prismatic lens is tobe cut,

. In sotar as I amaware, there are atthe present time two general processes for the production of prismatic ophthalmic lenses,

namely, grinding by hand and'decentration.

. In the. first process, that of grinding by hand, it is, necessary for the operator to take a lens, ground to power, and by constantly increasing the pressure as he draws the same over agrind-stone, grind therein a prism of the desired power. It is obvious that it requires considerable skill to produce the prism of the power desired and to keep the power. of the lens at the desired degree at all the points. is not only tedious, but requires considerable time when prisms of any great power must be ground.

Thesecond process, that of decentration, depends iorits basis upon the rule that any lens is capable of producing as many prism diopters as the lens possesses dioptersmor" retraction, provided itisdecentered 1 centimeter. To this rule there may be added that the prism diopters will increase or decrease proportionally as, the decentration becomes greater or lessQ From this it may easily be seen that a prism of practically any power-may beproduced in a lens of any power, provided there is sutlicient room for the necessary decentration.

As a few examples, it may be seen that a lens of one diopter it decentered one centimeter would give a prism of one prism diopter; a lens of two diopters decentered one centimeter would give two prism diopters, and so on, the prlsm dlopter being the unit prismatic retraction, and being equal to a deflection of one centimeter 'at a distance of one meter from the lens.

It is obvious'thatthe production of prismatic lenses by decentration is by far the more expedient and simple process of the two, although it too has certain drawbacks which have prevented it from becoming the exclusive process. It is awell known fact to those skilled in the art of ophthalmiclens In addition, this process manufacture that as we depart from theop tical center of an ophthalmic lens the power of the lens changes owing to the obliquity of the rays and to the prism angle or the lens. lVhile a lens may be ground to some one definite power at its center, a measurement of V the powers n any two planes at any point ofi' the center oi the lens Wlll show a variation from this central power dependent upon the distance of this point from the optical center, the shape of the lens, the power oi? the lens, theindex of refraction of the glass used, the center thickness of the lens, and the direction from which light enters the lens. liroin this it may readily be seen that ii we produce a. prisn'iatic lens by decentration.thatlalthough we may grind our blank to the power which we desire at its opti a1 center when we decenter and cut our linished prismatic lens about a new center, we obtain as the geometrical center of our finished lens, a point which dii'l'ers in power from the power which we desire. In other words, we will obtain a lens whose geometrical center varies from the power of the optical center of our lens and, therefore, from the power which we originally desired to obtain.

1t luzcoincs, therefore, a. most im iortant object of my invention to provide a process whereby we may produce a prisniaite lens whose geometrical center has the power which we desire. by a series of six steps, which I have diagrammatically shown in the drawing, each figure thereof representing a successive step in the process.

Referring now particularly to Figure 1, and tracing first the process through in a. general manner, I have shown a lens blank 10, in which I have located the focal center 11. Through this focal center 11, I may imagine the two meridians l2 and 11-5. F or the sake of clearness in this description I will consider the blank for this general process as spherical, although my process may he applied to a lens of any shape desired.

Haring been given some definite power which I desire to obtain in-niy completed lens, and also somedelinite amount of prism diopter, I locate, as shown in Figure 2, the point 1% which is to become the geometrical center of my finished prismatic lens, and whose position is determined by the amount oi. deeentration necessary to produce the prism diopter desired, and by the relative position in which I want the base of my prism to lie. Although I have shown it in this instance to be on the horizontal meridian, it is obvious that should I desire niy prism to be base up or base down the point 14' would be located on the vertical meridian either above. or "below the center line.

Haring thus computed the location of the point 14,1. proceed by well known trigonoiuetrical calculations, to compute for this point its amount of departure. from the axial power. I preferably compute these quantities in two planes, as shown in Figure 3, one plane being represented by the line 15, called the secondary plane, and the other plane by the line 16, called the primary plane. Having obtained the departure, then, of this point from the axial power of the blank, I

.l: accomplisa my process of 8.7 base out.

proceed, as in Figure l, to compensate for these errors by adding the inverse of these quantities to the axial power of the blank. For example, should 1 lind by calculation that the power at the point l t in the plane designated by the line to is too great by one halt a dioplcr, I should require a lens blank at whose optical center alongthe line shown at 17 in Figure 4, the power reduced by an amount equal to this, or, one halt a diopter, and similarly in the plane designated as 16 in Figure 3, should the error in this be, we will say, minus one half a dioptcr, 11 should require a greater power in my lens blank at its optical center in the plane designated by the numeral '18 in Figure 4, by one half a diopter. 'lly so modifying the power of the blank, at its optical center, the errors at the point l i which occur in the oplhalinicuse oi the lens are compensated.

Having thus found by i :alculatio1'1 the powers which I. must form on my lens at its optical center. l grind my blank, as showu in Figure to the new corrected power. in this way it will be seen that by producing, a blank with a substantially incorrect optical center, I obtain at the selected point des' nated by the numeral 14, those powers which 1 originally desired to obtain in my linishcd lens.

In Figure 3, I have shown the last and final stepin my process, which consists in cutting about the point 1'11: a completed lens 19. which shall have the prism dioptcr and refractive diopter desired. In. order now to more clearly show my pri'icerss as applied to a specific-examine, I will trace the same through the diagrammatic representation in the drawings when applied to a specific prescription.

Let us consider that we have been given a prescription calling for a lens for the right eye, having the power +71) sphere, 8.75 prism base out, the same'to be ground with a rear surface of: 4.001), a center thickness of nnnpand of a glass whose index at refraction equals 1.523. From this information, we are able to compute by mathematiical means, that curve. which placed on the front surface of the blank will give a lens of l-TD sphere. The power ol. the curve to be placed on the front surface oi the blank. computed from thepower oil. the curve ol' the rear surface of the blank, the center thickness desired in the finished lens, and the index of rcfractiono't the glass, and

happens to he in this particular case -l-1().(i7D.

Having thus determined the power of the curve to be placed on the front surface of my lens blank in order to give me a lens of +71) sphere, I proceed to consider how I am to include in my finished lens a prism Since I am to obtain this prism by cutting mylinished leusaboult a l ii t ll

lul

decentered point as a geometrical center, I spherical curvewhich I ordinarily would proceed to locate this point which is to be have placed on the front surface of my blank the geometrical center of my finished lens, to give me a lens of +71) sphere I must the same being diagrann'natically shown in substitute for this surface, a toric surface a 5 Figure 2 of the drawing and being desigof the curve +1018 sphere combined with nated by the numeral lt. 0.33 cyliiuleraxis 180 degrees. 3y grind- By right cyebase out, it is understood ing this toric surface on the front surface that the prescription calls for a prism with Many lens blank, I obtain at a point 125 its base or thickest portion on a horizontal c. m. to the leftof the'optieal axis, an in H- meridian, to the right of a line running creasein strengthof 0.4191) in the horizontal through the center of the lens blank. Iiad direction and 0.161) in the vertical directhe prescril'it-ion stated base up orbase down, tion. It is obvious, therefore, that this point it would have specified a prism whose base willn'ieasure +7001) sphere as required. or thickest portion was on av vertical merid- Having thus determinedthe surface which ian either above or below thecenter line of I must place on the front of my lens blank.

the lens. It, therefore, my prism is to be in order to give me the ultimate power debase outon a lens for the right eye, point sired at the geometrical center of my finished 14 must be located on the horizontal merid lens, I proceed to grii'idthe same asrepreian 13 to the right of the meridian 12, and sented in Figure 5, to the corrected power. 2 its decentration must be determined by the subsequently cutting from the blank, as rule that a lens of 1D decentered 1 ccnticlearly shown in Figure 6, a'completed lens meter gives a prism of one prism diopter. I having the poi at ll as its geometrical center. compute the amount of this decentration, In practical use, Ihave found that with therefore, by solving the following simple my invention, I can regulate the error in equation: 7I) Y=8.75. 3 the power at the geometrical center of my In the equation, TI) represents thepower prismatic lens to an amount less by far than of lens in diopters, Y is the unknown quan the difference inpowcr between neighboring tity, which represents the amount of deccnlenses in the'range series which is a practration necessary in centimeters required to tical' standard to use as itbrings the error produce the desired prism, and the 8.75 is within limits that may easily be accepted. the number of prism diopters. Solving then If myerror of prism diopter does not origfor Y which is to give me the amount of inally exceed this diii'erence between the decentration in centimeters, Iobtain 1.25 and neighboring lenses in the series, I prefer not thus locate the point 1a a distance of to correct the same, applying my process V centimeters from the optical center of my only when this error exceeds this difference blank. V at which time I am able by my process to- If new, I compute by trigonometric calso reduce the same as to make it practically culation, the power this point in the secnegligible. ondary plane 15 and the primary plane 10, In referring to the range series, I mean I shall find that in the plane 15 I would the series of ditii'erentpowcrs of lenses usualhave, instead of the power +71), which rcply ground or carried by all lens manufac-' resents the actual power which I desire, the turers. As illustrating aseries or range of power +1169, or an exe 5s power of plus commercial ophthalmic lenses, the following .101). In the primary planedesignatcd by schedule taken'fi'om the price list of one of 16, I would find a power of +7.49D or an the largestlens manufactures is set out: increase in power in this plane over the origspherical, 0.12, 0.25, 0.37, 0.50, 0.62, 0.75,

inal +7D which I desired of +401). 1.00, 1.25, 1.50, 1.75, 2.00, 2.25, 2.50, 2.75, 3.00,

In order then to correct this error, I add 3.25, 20.00.

to the central power of my lens blank the Cylinders and torics, 0.12, 0.25, 0.37, 0.50, i inverse of these errors. Referring now to 0.62, 0.75, 087, 1.00, 1.12, 1.25, 1.37, 1.50, 1.62, 115

Figure 4 of the drawing and considering 1.75, 2.00, 2.25, 6.50, 7.00, 7.50, 8.00. that I have added the inverse of these errors In the spherical range, it will be seen that to the original powers of the meridians 12- the lenses increase from 0.12 to 0.75 A;D and 13 at point 11, I find that I shall resteps, while as the lenses increase in power quire in the vertical meridian 17, a power the steps between the lenses increase, in

of plus 6.811) and in the horizontal meridian, reality, up to steps of 2 diopters. designated by the numeral 18, a power of In the cylinder or toric range the steps vary +6511), in that I have added to the vertical fron'i 1) to 2D similarly. I find that in meridian O.16D to decrease the power in producing prismatic lenses by decentration, the secondary plane at the point 14, and it is hardly practical to attempt to decenter a have added 0.49D to the horizontal nielens whose power is very low and that, thereridian to decrease the power in the primary fore, I need only make sure that my. correc plane at the point 14. tion is within 4D of the desired power, or From the foregoing computation, it is to an amount which represents the size of the be seen that in place of the original +1067 D steps in the range of average power lenses.

From the foregoing description it will he seen that I have provided a process by which prismatic ophthalmic lenses maybe produced through the grinding of a lens blank and the decentration of the same. i I have overcome the previous undesirability of this process in that I have provided means for correcting the error usually incident to lenses produced in this way. Should I care to stop my process at a point represented by l igure in the drawing, it will be seen that I will have produced a lens blank which has been ground to a power from which may be cut a substantially correct prismatic lens, and I. therefore, reserve the right to include such lens blanks within the spirit of my invention. i

While I have shown and described specific examples and details of my invention, it is to be understood that I do not desire to limit myself particularly thereto, in that I reserve the right to make certain departures in so far as I remain within the spirit of my invention and the scope of the appended claims.

Having thus described my invention, I claim: i

11.. The process of correcting for spherical and astigmatic error in a prismatic lens produced by decentration, which consists in varying the axial power of the lens blank from which the lens is to be cut to correct the power of the geometrical center of the finished lens.

The process of correcting for spherical and astigmatic error in a prismatic lens produced by decentration, which consists in adding an error to the axial power of the lens blank from which the finished lens is to be cut of a magnitude to correct the inherent error in the geometrical center of the finished lens. v

23. The process of correcting for spherical and astigmatic error in a prismatic lens produced by decentration, which consists in adding to the axial power of the blank from which the finished lens is to be cut the inverse of the marginal variation from axial power of a point in the lens blank coincident with the geon'ietrical center of the finished lens.

4. The process of producing a lens blank for an ophthalmic prismatic lens corrected for spherical and astigmatic error and pro duc'ed by decentration which consists in forming a blank with a power at its optical center corrected by the inverse of the amount of variation in power from this center, of: a marginal point adapted to be the geometrical center of the con'ipleted lens.

5. The process of producing an ophthalmic lens of any given power, havin g a prism of any given power produced by decent "a tion and corrected for spherical'and astigmatic error which consists in locating the optical center of a lens blank, locating the point on the lens blank which is to be the geometrical center of the prismatic lens, computing in two meridians the variation of this point from the power at the optical center of the lens blank, adding the inverse of this variation to the original power at the optical center of the lens blank, grindingthe blank to the corrected power at its optical center, and cutting the prismatic lens with the corrected point as its geometrical center.

6. An ophthalmic lens having the axial power exceeding the original calculated axial power by an amount equal to the inverse of the variation in power at the geometrical center of the lens in two meridians from the original calculated axial power of the lens.

7. An ophthalmic lens having the axial power exceeding the original calculated axial power by an amount equal to the inverse of the variation in power at the geometrical center of the lens from the original calculated axial power of the lens.

ANNA ESTELLE GLANCY. 

